In the medical field, it is frequently necessary after surgery or after a patient has incurred a trauma to the chest cavity to collect fluids from the chest cavity after the cavity has been closed. This type of fluid collection is commonly referred to as "closed-wound drainage". One particularly important feature of closed-wound drainage is that it requires a relatively low vacuum to suction fluids from the patient's chest cavity. If higher vacuums are used, damage to the internal organs may occur. Typical vacuum ranges of 20-30 cm. H.sub.2 O are used to collect fluids from a closed chest or pleural cavity.
Systems have been developed in the past which are specifically used to collect such fluids. One goal in suctioning or draining fluids from a chest cavity is to insure that air is not inadvertently returned to the chest cavity through the tube which is draining fluids from the patient. Accordingly, it is desirable to provide a one-way check valve or other system to insure one-way flow of fluids and gases from the patient to a collection container.
Various systems have been used in the past to collect fluids from a chest cavity. One system uses a rigid cannister with a flexible liner. In this particular system, the vacuum applied to the inside of the liner is equal to the vacuum applied between the liner and the cannister. One problem with this system is that the liner may not completely expand to fit the inside of the cannister. If the liner is folded inside the cannister, it is difficult for medical personnel to accurately monitor the amount of fluids that are collected in the liner. Therefore, a need exists to provide a system which insures that the liner completely expands within the cannister to rest against the walls of the cannister to allow medical personnel to more readily view and measure the contents of the fluids in the liner.
Another system has been developed which uses a rigid cannister and a flexible liner but which applies a high-vacuum between the cannister and the liner when the system is initially put together to be used. Once the bag is expanded, the high-vacuum source is removed from the cannister and a low-vacuum source is applied to the inside of the liner. In this system, an elastomer check valve is provided to prevent leakage of the high-vacuum between the liner and the cannister. However, in some instances, leakage may occur. This leakage will allow the liner to collapse upon itself as the low-vacuum is applied to the inside of the liner to suction fluids from a patient. When this occurs, it is necessary for medical personnel to re-apply a high-vacuum source to the space between the liner and the cannister. This has been considered to be a nuisance and it is, therefore, accordingly desirable to develop a new system which does not require the re-application of a high-vacuum between the liner and the cannister.
Another goal in pleural drainage systems is to insure that any accidental high-vacuum present in the liner of a pleural drainage system is not introduced to the patient's pleural cavity. An accidental high-vacuum in the liner may occur when medical personnel performs "milking" of the drainage tube between the patient and the liner. Milking is the act of releasing clots formed in the drainage tube by sequentially squeezing and pulling sections of the tube to force clots that exist in the tube down into the liner. This action may inadvertently cause a temporary high vacuum to exist in the liner and thus exist in the drainage tube. Therefore, a need exists to provide a system which has a sensing mechanism for determining when the vacuum in the liner exceeds a pre-determined level.